Rubble in the wake of the devastating Alabama tornado outbreak on April 27, from Tuscaloosa. (NOAA)

In a year marked by a relentless assault of extreme weather, several events stand out. Some, like the tornado that leveled Joplin, Missouri on May 22. were extraordinarily devastating and deadly. Others - such as the “Snowtober” storm that buried the Northeast under a crushing load of heavy, wet snow - were downright freakish. In a typical weather year, one might expect a few extreme events like these.

But this was no ordinary year. At times it seemed as if Mother Nature was on steroids, slamming Americans with one deadly event after another (a good case can be made that Mother Nature is, in fact, on steroids, thanks to global warming). Consider this: according to NOAA, there were at least 12 events that cost a billion dollars or more, an all-time record (there were 14 such events by other measures). More than 1,000 people died from weather-related causes this year, most of them from tornadoes, and more than 8,000 people were injured, according to the National Weather Service.

As we’ve covered on this blog, scientific research shows that global warming is likely increasing the odds and severity of certain extreme events, such as heat waves and heavy precipitation events. These aren’t exactly comforting findings, given what transpired this year.

Here are the top 5 extreme weather events of 2011.

Aerial view of damage from April 27, Tuscaloosa tornado (NOAA)

This was the year of the twister, and multiple tornado outbreaks exacted a heavy price in terms of lives lost. The death toll from many of this year’s tornadoes were so high (tied for second highest on record) that the National Weather Service has embarked on a broad-scale effort to reexamine how it educates the public about tornado risks, and how tornado warnings are worded and disseminated.

On that day, major tornadoes tore through the cities of Tuscaloosa and Birmingham, and all-but wiped out many rural communities. The Tuscaloosa-Birmingham EF-4 tornado was on the ground for more than 80 miles, and seven other tornadoes stayed on the ground for at least 50 miles.

April 2011 now ranks as the most active tornado month on record with 753 tornadoes, beating the previous record of 542 tornadoes set in May 2003. NOAA has put the total number of April tornado-related fatalities at 364.

The most intense tornadoes flattened some communities. Here’s what a Weather Service storm damage assessment team found in the small town of Phil Campbell, Alabama, after a tornado tore through there on April 27th.

Along Bonner Street, multiple block homes were leveled to the ground with the block foundations destroyed. A twenty-five foot section of pavement was sucked up and scattered. Chunks of the pavement were found in a home over 1/3 of a mile down the road. The damage in this area was consistent with EF-5 damage.

2. Joplin, Missouri EF-5 Tornado

Radar image of thunderstorm that spawned the catastrophic May 22 Joplin tornado. The bright pink area, or “debris ball” shows where the radar was sensing debris from the tornado.

The tornado was part of a larger, multi-day outbreak during which 180 tornadoes touched down in the central and southern states, resulting in more than $9.1 billion in total losses, according to NOAA.

3. The Triple Threat of Drought, Heat and Wildfires

One of the costliest natural disasters of the year evolved over a longer timespan and across broader geographic region, as drought conditions parched the Texas landscape and portions of Oklahoma, New Mexico, Arizona, Kansas and Louisiana. In Texas, the drought was the most intense one-year drought on record, with direct losses to crops, livestock and timber of close to $10 billion.

The drought was aggravated by record heat, with many locations across the Southern Plains setting records for the most 100-degree days, including San Angelo, Texas, which reached the century mark on 98 days this year. Oklahoma had the hottest summer of any state in American history, just edging out Texas, which came in second. Oklahoma’s average July temperature was 88.9 degrees, making it the warmest month in any state on record.

The dry conditions forced ranchers to send their cattle to the slaughterhouse early. According to recent reports, 2011 saw the largest-ever one-year decrease in the number of Texas cattle, a loss of about 600,000 cattle in just one year. This may translate to higher beef prices in 2012, due to a below average supply.

The drought and heat also set the stage for the worst wildfires in Texas state history, including the Bastrop fire, which was the state’s most destructive wildfire on record. Wildfires also charred vast stretches of Arizona, New Mexico and Oklahoma. In fact, Arizona and New Mexico both saw their largest wildfires on record. At one point, the Las Conchas Fire in New Mexico, which burned over 150,000 acres, threatened the Los Alamos National Laboratory, the birthplace of the atomic bomb.

Nevertheless, Irene managed to grind life to a halt in the city that never sleeps - with the first ever shutdown of mass transit, including all three airports, and mandatory evacuations of people from vulnerable parts of the city. Because the storm was weaker than expected when it struck the city - as a tropical storm rather than a hurricane - the damage was far less than feared. However, as Jeff Masters has detailed at Weather Underground, the lack of damage in New York City should not be taken as a sign that the city is safe from such storms.

Irene reserved her worst for a sneak attack on inland areas. After an extremely wet summer, Irene’s rains caused record flooding in New Jersey, New York and Vermont. Many of Vermont’s iconic covered bridges were washed away, and entire communities became cut off from transportation routes. The storm also caused massive power outages, with upwards of seven million homes and businesses without power at the height of the storm, according to NOAA.

NASA satellite image showing “Snowtober” pulling away into the Atlantic, with an extensive snow cover from Vermont to West Virginia. (NASA)

Just as the Northeast was beginning to bounce back from Irene, the region was walloped by an early season winter storm that rewrote the history books. Heavy snow fell at a time when most trees still had most of their leaves; causing widespread power outages that in at least one state - Connecticut - eclipsed the outages caused by Irene. As I wrote on this blog:

To put the storm into its proper meteorological context, consider these snowy facts. The storm brought thundersnow to New York City shortly past lunchtime on Saturday, October 29, before the city had even recorded its first freeze. Central Park received 2.9 inches of snow, with up to six inches falling in the Bronx. This was the only time in recorded history that an inch or more of snow has fallen in Central Park during the month of October.

Jaffrey, New Hampshire, recorded 31.4 inches of snow, and 32 inches fell in Peru, Mass. In Concord, N.H., 22.5 inches fell in just 16 hours. October snowfall records were smashed in Hartford, Connecticut, which received 12.3 inches; Worcester, Mass., where 14.6 inches fell; and Newark, NJ, where 5.2 inches piled up.

The timing of this storm made it a high impact event, although it would have been noteworthy for its intensity and heavy snowfall even if it had occurred in February.

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